[Bug tree-optimization/102546] Missed Dead Code Elimination regression (trunk vs 11.2.0) at -O3

["aldyh at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102546

Aldy Hernandez <aldyh at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |aldyh at gcc dot gnu.org,
                   |                            |amacleod at redhat dot com

--- Comment #2 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
By VRP1 we seem to be calculating the following:

(f_8 << f_8) && (f_8 == 0)

This would fold to false, which would elide the foo():

 <bb 7> [local count: 59055800]:
  b = 0;
  _3 = f_8 << f_8;
  _4 = (char) _3;
  _5 = (int) _4;
  if (_4 > 0)
    goto <bb 8>; [64.06%]
  else
    goto <bb 10>; [35.94%]

  <bb 8> [local count: 34842922]:
  if (f_8 == 0)
    goto <bb 9>; [71.10%]
  else
    goto <bb 10>; [28.90%]

  <bb 9> [local count: 12809203]:
  foo ();

So from the outset, it seems like this is a missing relation in range-ops. 
That is if we know f_8 << f_8 is non-zero, then we know f_8 cannot be 0.  This
looks like an easy fix, however...

What I fail to see is how "a" got removed entirely from the IL, making this
scenario possible:

 if (!(a >= d || f))
            foo();

Am I missing something obvious here?